Conventionally, a technique for supporting a driver of a vehicle towing a trailer to change a direction is well known. For example, JP-A-2006-27343 teaches a vehicular device for determining, whether it is possible for the vehicle with the trailer to change in direction at a next corner on a road ahead, according to a road shape stored in a map data of a navigation device and a minimum turning radius of the vehicle with the trailer, which is preliminary set. Further, the vehicular device outputs warning to the driver when it is impossible to change in direction at the next corner. Further, when it is impossible to change in direction at the next corner, the vehicular device warns the driver, and outputs a warning message to the driver in order to prompt the driver to change in direction at the corner with a large turning radius of the towing vehicle.
However, the technique disclosed in JP-A-2006-27343 merely outputs the warning information before changing in direction at the next corner. Accordingly, if the vehicle and/or the trailer run over a road region (i.e., a driving allowance region), which is allowed for the driver to run through after the driver starts to change in direction at the next corner, it is difficult to support the driver to restrict the running over, i.e., it is difficult to avoid to drive along an outside of the driving allowance region.
It is considered that a driving support device restricts to run over the driving allowance region by supporting the driver to drive the towing vehicle with the trailer along a stored trajectory of a towing vehicle based on stored information. The stored trajectory in the stored information is previously obtained from the towing vehicle, which does change in direction at the corner without running over the driving allowance region.
However, even if the behavior of the towing vehicle is the same, the behavior of the trailer may be different when the load of the trailer is different. Thus, even if the driving support device supports the driver in the above manner, the vehicle with the trailer may run over the driving allowance region while the vehicle change in direction at the corner.